I updated my beowulf VM last night and my wallpaper went poof. I am
unable to select any image from the desktop settings or from r-click
option on the image or with drag-n-drop from /home or /usr. That
function is now doa. I was able to set a gradient.

I searched the xfce forum and found this old thread that had a response
just last year:

https://forum.xfce.org/viewtopic.php?id=5235

Looks like something isn't registering with session management/dbus.
Hope you can find what broke it. FWIW, selecting wallpaper images on
beowulf has always been iffy but until now I've managed to find a way.
Jessie and ascii were fine.

Happy hunting!

golinux